It is well known that the ionosphere can be highly disturbed in the auroral and polar cap regions. However, efforts to quantify ionospheric effects on high-frequency communications have concentrated mainly on lower-latitude regions. The Doppler and multipath sounding network (DAMSON) has been used in an extensive campaign to measure the channel characteristics on four paths in the auroral region of northern Scandinavia. The conditions observed indicate that robust data modems, used when less-robust, higher-rate modems fail, are required up to 90% of the time. A detailed analysis of the propagation parameters indicates that these modems, designed to operate in these regions, should be able to operate when the Doppler spread exceeds 40 Hz and the multipath spread is greater than 11.5 ms. Multiple propagation modes are common, especially between the lowest and maximum usable frequencies. The distribution of the received signal power in these cases is examined, and it is concluded that laboratory simulations used for robust-modem evaluation should include channel models with dominant modes.

The performance of beyond line-of-sight (BLOS) high frequency (HF) communication systems is dependent on how well the system is matched to the propagation environment. In this respect issues such as antenna gain and transmitter power are very important. Deserving equal or greater attention, however, is the issue of the match between the signalling waveform and the time and frequency spread characteristics of the propagation path. This paper briefly describes a channel sounder known as DAMSON (Doppler and multipath sounding network) which has been developed to characterise the disturbed narrow band channel (3 kHz) by measuring its scattering function. The real time nature of the DAMSON processing makes it unique in the frequency range but, in its approach to measuring the channel its operation is similar to that of Wagner et al. (1988). (5 pages)